1. Field of the Invention
The present invention relates to a transmission line incorporated in an electronic device, and particularly to a composite transmission line provided with a plurality of lines, and an electronic device provided with such a composite transmission line.
2. Description of the Related Art
Conventionally, various kinds of transmission lines that transmit a high frequency signal have been devised. For example, Japanese Patent Laid-Open publication No. 2014-179297 discloses a multiple-conductor flat cable that has an analog signal line and a digital signal line. The multiple-conductor flat cable includes an analog cable portion formed such that a plurality of ground signal lines and a plurality of analog signal lines are alternately arranged side by side across a signal transmission direction and each pair of the ground signal lines and the analog signal lines are joined while being electrically insulated from each other. In addition, a digital cable portion is formed such that a plurality of digital signal lines are arranged side by side across the signal transmission direction and each pair of the digital signal lines are connected while being electrically insulated from each other. Further, the analog cable portion and the digital cable portion are arranged in parallel to each other in an unfolded state, and the analog cable portion is rolled up or folded in a direction across the signal transmission direction so as to cover the digital cable portion.
In such a conventional multiple-conductor flat cable disclosed in Japanese Patent Laid-Open publication No. 2014-179297, necessary signal lines are combined to configure a cable that individually transmits various kinds of signals.
The multiple-conductor flat cable that transmits various kinds of signals is capable of transmitting the various kinds of signals by one cable and is thus also useful as a component in an electronic device that is required to be small in size. For example, a plurality of circuit boards are incorporated in the housing of an electronic device, and the plurality of circuit boards are connected by a multiple-conductor flat cable.
In a case in which not only signal transmission but also power transmission is performed in a small transmission line incorporated in the housing of such an electronic device, in a transmission line that transmits various kinds of signals, it is important to prevent the size (thickness and width) from increasing and to also significantly reduce interference between lines.